This application relates to nonaqueous electrolyte batteries and nonaqueous electrolytes, specifically to nonaqueous electrolyte batteries and to nonaqueous electrolytes that include an organic solvent and an electrolyte salt and used for nonaqueous electrolyte batteries.
Efforts have been made to reduce the size and weight of portable electronic devices such as camera-integrated VTRs, digital still cameras, cell phones, personal digital assistances, and laptop computers. In this connection, there has been active research and development to improve the energy density of batteries, particularly secondary batteries, used as the portable power source of such electronic devices.
Lithium ion secondary batteries that use carbon, a lithium-transition metal composite oxide, and a carbonate ester mixture for the negative electrode active material, the positive electrode active material, and the electrolytic solution, respectively, have been put to a wide range of practical applications for their ability to provide greater energy density than other nonaqueous electrolytic solution secondary batteries such as lead batteries and nickel cadmium batteries.
Laminated lithium ion secondary batteries that use an aluminum laminate film for the exterior particularly have high energy density because of lightness. Laminated polymer lithium ion secondary batteries also have widespread use among the laminated lithium ion secondary batteries, because the polymer used for the battery swells with the electrolytic solution, and suppresses deformation of the laminated battery.
Increasing the thickness of the active material layer for higher capacity increases the amount of current per area density during charging, and the lithium ions cannot be inserted into the negative electrode active material in time. This has caused problems such as deposition of lithium metal on the negative electrode surface, and low percentage of remaining discharge capacity during repeated charge and discharge. As a solution for these problems, JP-A-2009-206073 (Patent Document 1) and JP-A-2007-188861 (Patent Document 2) propose suppressing decomposition of the electrolytic solution and thus improving charge and discharge cycle characteristics with the use of a protective coating formed on the negative electrode surface by adding, for example, halogenated cyclic carbonate or unsaturated cyclic carbonate to the electrolytic solution.
The materials used as the positive electrode active material of secondary batteries have, for example, a layered rock-salt crystal structure represented by the general Formula LixMO2, such as lithium cobalt oxide (where M is at least one selected from aluminum (Al), manganese (Mn), cobalt (Co), and nickel (Ni). The composition of such positive electrode active material in the fully charged state is generally LixMO2 (x=0.5). However, batteries that have compositions with x<0.5 during charging have also been developed for higher capacity. Techniques currently available to realize x less than 0.5 use either a nickel (Ni) content of 75% or more in the transition metal M under a charge voltage of 4.2 V, or a charge voltage of 4.3 V or more.